hash of hashes

[Paul Argentoff]

Hi all.

How can I create $Subject for future population?

 

[Paul Argentoff]

How can I create $Subject for future population?

Let's put it this way: I need to create a nested hash which will be populated
later by referencing the keys in the subhashes. How can I do this?

 

[Emmanuel Touzery]

Let's put it this way: I need to create a nested hash which will be populated
later by referencing the keys in the subhashes. How can I do this?

not sure i understand your question. does this help you?

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

 

[Paul Argentoff]

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

I need something like this:

a = {{}} # this doesn't work, but i've just written it here to emph. the
# subject
...
# somewhere in the iteration
a[foo][bar] = baz
...

 

[Emmanuel Touzery]

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

I need something like this:

a = {{}} # this doesn't work, but i've just written it here to emph. the
# subject
...
# somewhere in the iteration
a[foo][bar] = baz
...

i think you need ruby 1.8's block form for creating hashes. i asked that
question recently, and here is the snippet from Guy Decoux:

svg% ruby -e 'has = Hash.new {|h,k| h[k]={}}; has["blue"]["red"] = 1; p has'
{"blue"=>{"red"=>1}}
svg%

 

[Paul Argentoff]

not sure i understand your question. does this help you?

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

Here is my example:

irb(main):008:0> a = Hash.new(Hash.new(Array.new(2,0)))
=> {}
irb(main):009:0> a['foo']['bar'][1] = 2
=> 2
irb(main):010:0> a['foo']['bar']
=> [0, 2]
irb(main):011:0> a.keys
=> []
irb(main):012:0>

After this I can't iterate over a's keys -- what I've written the whole mess
for

 

[Joel VanderWerf]

Paul Argentoff wrote:
...

I need something like this:

a = {{}} # this doesn't work, but i've just written it here to emph. the
# subject
...
# somewhere in the iteration
a[foo][bar] = baz
...

hash_maker = proc do |h, k|
h[k] = Hash.new(&hash_maker)
end

h = Hash.new(&hash_maker)

h[1][2][3][4][5] = 6

p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

 

[Paul Argentoff]

hash_maker = proc do |h, k|
   h[k] = Hash.new(&hash_maker)
end

)) Exmaple is worthy of a Haskell tutorial ))

The problem is, afaik, that I tried to do THAT with Ruby 1.6 :-/

 

[Dave Brown]

:
: > How can I create $Subject for future population?
:
: Let's put it this way: I need to create a nested hash which will be populated
: later by referencing the keys in the subhashes. How can I do this?

You mean, er,

irb(main):001:0> a=Hash.new({})
=> {}
irb(main):002:0> a['foo']
=> {}

?

--Dave

 

[Joel VanderWerf]

:
: > How can I create $Subject for future population?
:
: Let's put it this way: I need to create a nested hash which will be populated
: later by referencing the keys in the subhashes. How can I do this?

You mean, er,

irb(main):001:0> a=Hash.new({})
=> {}
irb(main):002:0> a['foo']
=> {}

?

--Dave

That's like, a real bad trip, dude:

irb(main):002:0> a=Hash.new({})
=> {}
irb(main):003:0> a[1]
=> {}
irb(main):004:0> a[1]["x"] = "y"
=> "y"
irb(main):005:0> a
=> {}
irb(main):006:0> a[1]
=> {"x"=>"y"}
irb(main):007:0> a[1] = 2
=> 2
irb(main):008:0> a[2]
=> {"x"=>"y"}
irb(main):009:0> a[1]
=> 2

It would help to do

a = Hash.new {{}}

since you get a new hash each time...

 

[Martin DeMello]

hash_maker = proc do |h, k|
h[k] = Hash.new(&hash_maker)
end

h = Hash.new(&hash_maker)

h[1][2][3][4][5] = 6

p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

My head hurts That needs to go on the Ruby Idioms page.

martin

 

[Simon Strandgaard]

hash_maker = proc do |h, k|
h[k] = Hash.new(&hash_maker)
end

h = Hash.new(&hash_maker)

h[1][2][3][4][5] = 6

p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

My head hurts That needs to go on the Ruby Idioms page.

Wew nice trick indeed

I have added it to the StandardClassExtension page:
http://www.rubygarden.org/ruby?StandardClassExtensions/Hash

 

[Robert Klemme]

not sure i understand your question. does this help you?

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

Here is my example:

irb(main):008:0> a = Hash.new(Hash.new(Array.new(2,0)))
=> {}
irb(main):009:0> a['foo']['bar'][1] = 2
=> 2
irb(main):010:0> a['foo']['bar']
=> [0, 2]
irb(main):011:0> a.keys
=> []
irb(main):012:0>

After this I can't iterate over a's keys -- what I've written the whole mess
for

That's because the form Hash.new( obj ) just replaces the nil return value
for keys that are not found. In your example you have a hash that returns a
hash for unknown keys that in turn returns an array for unknown keys. You
definitely need the block form. Or you have to wrap or sub class the hash
if you want to use pre 1.8 ruby versions.

Regards

robert

 

[Robert Klemme]

:
: > How can I create $Subject for future population?
:
: Let's put it this way: I need to create a nested hash which will be populated
: later by referencing the keys in the subhashes. How can I do this?

You mean, er,

irb(main):001:0> a=Hash.new({})
=> {}
irb(main):002:0> a['foo']
=> {}

?

--Dave

That's like, a real bad trip, dude:

irb(main):002:0> a=Hash.new({})
=> {}
irb(main):003:0> a[1]
=> {}
irb(main):004:0> a[1]["x"] = "y"
=> "y"
irb(main):005:0> a
=> {}
irb(main):006:0> a[1]
=> {"x"=>"y"}
irb(main):007:0> a[1] = 2
=> 2
irb(main):008:0> a[2]
=> {"x"=>"y"}
irb(main):009:0> a[1]
=> 2

It would help to do

a = Hash.new {{}}

since you get a new hash each time...

Not really:

irb(main):001:0> h=Hash.new{{}}
=> {}
irb(main):002:0> h[1][2]="foo"
=> "foo"
irb(main):003:0> h
=> {}
irb(main):004:0>

You need a = Hash.new {|h,k| h[k]={}} as pointed out already.

robert

 

[Joel VanderWerf]

Not really:

Oops. Of course you're right, since the value returned by the block is
never assigned to any part of the hash. You always have to do that yourself.

 

[Robert Klemme]

Oops. Of course you're right, since the value returned by the block is
never assigned to any part of the hash. You always have to do that

yourself.

.... and it's always the same. Something not wanted in this case.

robert